Flocculation of suspended solids from aqueous solutions

ABSTRACT

The use as flocculants of aluminum chloride/water-soluble cationic polymer compositions having inorganic:polymer weight ratios of at least 5:1 is disclosed. These compositions are especially effective in low turbidity waters.

BACKGROUND OF THE INVENTION

This invention relates to methods of flocculating, accelerating the rate of flocculation and/or accelerating the settling of solids which are suspended in aqueous media by addition thereto of a flocculating composition.

U.S. Pat. No. 4,450,092 discloses compositions useful for coagulating finely divided solids in turbid waters. These compositions are prepared by mixing inorganic water-soluble compounds such as aluminum chloride, aluminum sulfate, ferric chloride and ferric sulfate with a polymer of diallyl dimethyl ammonium chloride having a molecular weight of at least 2,000. The weight ratio of the inorganic component to the organic component ranges from 0.75:1 to about 4:1.

U.S. Pat. No. 4,582,627 discloses flocculating agents which are reaction products of sulfate ion-containing polymeric aluminum hydroxy chloride and one or more cationic polymers such as polyacrylic amide, polyamide amine and polyethylene imine.

U.S. Pat. No. 4,137,165 discloses the use of low molecular weight acrylamide polymers which contain quaternized dimethylamino methyl groups for clarification of turbid waters.

U.S. Pat. No. 3,489,681 discloses the use of water-soluble copolymers of diacetone acrylamide as flocculating agents.

The term flocculation, as used herein, is synonymous with the term coagulation. Flocculation refers to the settling of suspended solid particles from aqueous systems. Turbidity, as used herein, is defined as the cloudiness or haziness of a solution caused by finely suspended particles. Turbidity is meausred using NTU's, (nephelometric turbidity units). As used herein, low turbidity systems are systems having a low solids concentration (on a weight basis), i.e., a solids weight percent of 0.1 or less. As a general rule, this corresponds to an approximate turbidity of 50 NTU's or less, but may vary do to nature of the solids or dissolved colored matter. High solids suspensions include those systems containing in excess of 0.1 weight percent suspended solids, which generally corresponds to a turbidity of greater than 50 NTU's. While the instant compositions are especially effective in low turbidity waters, it is not intended that their use be so restricted. In fact, the instant compositions are useful in a wide variety of raw waters and in concentrated wastewaters.

Many flocculants are known, including alum (Al₂ (SO₄)₃ X H₂ O, wherein X is about 14), poly(aluminum chloride), sodium aluminate, iron compounds such as ferric chloride and ferric sulfate, lime and various cationic organic polymers, including but not limited to poly(alkaline amines), poly(diallyl dimethyl ammonium chloride), poly(2-hydroxy propyl-1-N-methyl ammonium chlorides) and quaterized poly(N-N-dimethylaminomethacrylate). The novel compositions of the instant invention are not, however, known or suggested in the art.

SUMMARY OF THE INVENTION

The instant invention relates to synergistic flocculation compositions of aluminum chloride and at least one water-soluble cationic polymer selected from the group consisting of water-soluble polyamines and water-soluble dialkyl diallyl ammonium polymers, wherein the weight ratio of aluminum chloride to polymer is at least 5:1, on an active basis.

Thus, the instant method utilizes a synergistic composition comprising aluminum chloride and at least one water-soluble cationic polymer to accomplish clarification objectives. The novel compositions of this invention are stable when blended together and synergistically settle fine suspended matter from aqueous systems. The instant compositions are especially effective in low-turbidity, low-alkalinity waters, but they are also effective in other waters. Low-alkalinity waters, as used herein, are waters having total alkalinity values of 150 ppm or less.

Additionally, the instant compositions are convenient to use since only one product must be added to the system being treated, instead of two or more.

DETAILED DESCRIPTION OF THE INVENTION

The instant invention relates to a composition useful for reducing turbidity in aqueous systems which comprises: (a) aluminum chloride; and (b) at least one water-soluble cationic polymer selected from the group consisting of water-soluble polyamines and water-soluble dialkyl diallyl ammonium polymers, wherein the weight ratio of (a) to (b) is at least 5:1, and preferably ranges from 10:1 to about 100:1, most preferably 10:1 to about 30:1.

Any water soluble polyamine may be used. As used herein, the term polyamine includes any water-soluble product having the following structure: ##STR1## wherein R₁ and R₂, which may be the same or different, are selected from the group consisting of C₁ -C₈ straight or branched alkyl, substituted C₁ -C₈ straight or branched alkyl and hydrogen and wherein R is selected from the group consisting of C₁ -C₈ straight or branched alkyl and substituted C₁ -C₈ straight or branched alkyl, and wherein n ranges from 2 to 50,000. Preferably, the molecular weight should range from about 500 to about 200,000, as determined by gel permeation chromatography. Polymers having molecular weights ranging from about 10,000-150,000 are more preferred. The most preferred polyamines are epichlorohydrin-dimethylamine polymers.

Any water soluble di C₁ -C₈ alkyl diallyl ammonium polymer can be used. The preferred polymers are polydimethyl diallyl ammonium chloride (polyDMDAAC), polydiethyldiallyl ammonium chloride (polyDEDAAC), polydimethyl diallyl ammonium bromide (polyDMDAAB) and polydiethyl diallyl ammonium bromide (polyDEDAAB). The most preferred dialkyl diallyl ammonium polymer is a homo polymer or dimethyl diallyl ammonium chloride.

The molecular weight of the dialkyl diallyl ammonium polymer preferably ranges from about 1,000 to about 5,000,000, as determined by gel permeation chromatography.

The ratio of aluminum chloride to polymer is critical, and should be at least 5:1, by weight, on an active basis. Preferably, the ratio should range from 10:1 to about 100:1, and most preferably from 10:1 to about 30:1. These compositions synergistically reduce turbidity in aqueous systems, particularly low-turbidity, (i.e., systems containing 0.1 or less weight percent of suspended solids), low-alkalinity systems (i.e., 150 ppm or less).

The instant invention is additionally directed to a method for reducing turbidity in an aqueous system which comprises adding to said system an effective amount of a composition comprising: (a) aluminum chloride; and (b) at least one cationic polymer as defined above; wherein the weight ratio of (a) to (b) is at least 5:1, preferably 10:1 to about 100:1, and most preferably 10:1 to about 30:1.

As used herein, the phrase "effective amount" refers to that amount of an aluminum chloride/polymer composition which is necessary to reduce turbidity in the system being treated. Generally, the effective amount will range from about 0.1 ppm of the instant compositions, on an active basis, to about 100 ppm of the instant compositions.

The key to this invention is that the inventors have discovered a synergistic relationship between aluminum chloride and certain cationic polymers. While use of these components, individually, is known in the art, the use of the instant compositions is not known. The synergistic benefit of the combined components, as demonstrated by the examples, is surprising and unexpected.

The instant compositions are especially effective in low turbidity, low alkalinity waters. However, the inventors do not intend that the instant compositions be restricted to use in such systems, as the instant compositions are effective flocculants in a wide range of aqueous systems.

Other important aspects of the instant invention are that the components of the compositions are compatible and that the instant compositions are stable. Additionally, the instant compositions afford the advantages of using one product instead of many products.

Preferably, the instant compositions are applied as aqueous solutions. Thus, an aluminum chloride/cationic polymer composition is added to water forming an aqueous solution. The maximum weight percent of the composition in water depends upon its solubility limit; generally, however, it is preferred that the aqueous solution contain from about 0.1 to about 20%, by weight, of the instant aluminum chloride/cationic polymer composition, wherein the weight ratio of aluminum chloride to cationic polymer is at least 5:1, on an active basis.

EXAMPLES

The following examples demonstrate the invention in greater detail. These examples are not intended to limit the scope of the invention in any way.

In the examples, the following products were used:

AlCl₃ is an aluminum chloride solution available from Hardwicke Chemical Company (which is 26-28% active (weight basis), with 2-5 weight % aluminum bromide), Reheis Chemical Company (28 weight % active), Courtney Industries (28 weight % active) or Vista Chemical Company (25 weight % active).

Alum is a 50% active aqueous solution of aluminum sulfate, Al₂ (SO₄)₃.14H₂ O.

High MW PolyDMDAAC is 20 weight % active polydimethyl diallyl ammonium chloride (MW=1,000,000-2,000,000), availabe from Calgon Corporation as Cat-Floc L.

Medium MW Poly DMDAAC is 20 weight % active polydimethyl diallyl ammonium chloride (MW=150,000±50,000), available from Calgon Corporation as Cat-Floc TL.

Low MW Poly DMDAAC is 30 weight % active polydimethyl diallyl ammonium chloride (MW=3,000-4,000), available from Calgon Corporation as Varikem 110.

Dry Poly DMDAAC is 100% active polydimethyl diallyl ammonium chloride (MW=approximately 200,000), available from Calgon Corporation as E-921.

High MW Polyamine is a 50 weight % active epichlorhydrin--dimethylamine polymer (MW=100,000), available from American Cyanamid as CA-260.

Low MW Polyamine is a 50 weight % active epichlorohydrin dimethylamine polymer (MW=20,000), available from American Cyanamid as CA-250.

Alum/Medium MW Poly DMDAAC (5:1) is Cat Floc K-5, available from Calgon Corporation, which is 5 parts, by weight, a 50% alum solution (by weight) and 1 part Catfloc C, a 40%, by weight, active polyDMDAAC having a molecular weight of approximately 150,000.

Alum/Medium MW Poly DMDAAC (10:1) is Cat Floc K-10, available from Calgon Corporation, which is 10 parts, by weight, a 50% alum solution (by weight) and 1 part Catfloc C, a 40%, by weight, active polyDMDAAC having a molecular weight of approximately 150,000.

EXAMPLES 1-29

In Examples 1-29, jar tests were run on Watauga River water having an initial turbidity of 4.0-4.5 NTU's. The water had a total alkalinity of 60-70 ppm.

The jar tests were run under the following conditions:

1 min @ 100 rpm

20 min @ 45 rpm

10 min @ 0 rpm

After a 10 minute settling period, 30 ml samples of supernatant were drawn, and turbidity was measured using a Bausch & Lomb Mini-20 Spectrophotometer/Nephelometer.

For filtration index measurements, 100 ml samples of supernatant were drawn, and the time was measured for each 100 ml sample to pass through a sheet of 0.3 micron filter paper. The filtration index values were then calculated by dividing the time obtained by the time required for 100 mls of deionized water to pass through a sheet of 0.3 micron filter paper.

Results are shown in Table I.

                  TABLE I                                                          ______________________________________                                         Exam-                As       Supernatant                                      ple                  Product  Clarity  Fil-                                    Num-                 Dosage   (NTU'S)  tration                                 ber   Flocculant     (ppm)    (10 min.)                                                                               Index                                   ______________________________________                                          1*   Alum           10       4.4      --                                       2*   Alum           15       4.0      2.37                                     3*   Alum           20       3.7      2.30                                     4*   Alum           30       2.4      2.22                                     5*   Alum           40       2.4      --                                       6*   Alum           50       2.9      --                                       7*   Alum/DMDAAC    10       4.3      --                                            (10:1)**                                                                  8*   Alum/DMDAAC    15       3.6      --                                            (10:1)                                                                    9*   Alum/DMDAAC    20       2.9      1.93                                          (10:1)                                                                    10*  Alum/DMDAAC    25       2.3      --                                            (10:1)                                                                    11*  AlCl.sub.3.sup.+                                                                              10       4.1      --                                       12*  AlCl.sub.3     15       3.9      1.96                                     13*  AlCl.sub.3     20       2.6      --                                       14*  AlCl.sub.3     25       2.2      1.63                                    15    AlCl.sub.3 /Low MW                                                                            10       3.5      --                                            Polyamine (5:1)                                                          16    AlCl.sub.3 /Low MW                                                                            15        1.75    1.30                                          Polyamine (5:1)                                                          17    AlCl.sub.3 /Low MW                                                                            20       1.4      1.26                                          Polyamine (5:1)                                                          18    AlCl.sub.3 /Low MW                                                                            25       1.4      --                                            Polyamine (5:1)                                                          19    AlCl.sub.3     15       3.8      1.96                                    20    AlCl.sub.3 /Low MW                                                                            15       1.9      1.22                                          Polyamine (5:1)                                                          21    AlCl.sub.3 /Low MW                                                                            15       1.7      1.26                                          Polyamine (10:1)                                                         22    AlCl.sub.3 /Low MW                                                                            15       2.3      1.48                                          Polyamine (20:1)                                                         23    AlCl.sub.3 /High MW                                                                           15       2.9      1.63                                          DMDAAC (5:1)                                                             24    AlCl.sub.3 /High MW                                                                           15       2.7      1.63                                          DMDAAC (10:1)                                                            25    AlCl.sub.3 /High MW                                                                           15       3.2      1.81                                          DMDAAC (20:1)                                                            26    AlCl.sub.3 /High MW                                                                           15       1.8      1.33                                          Polyamine (10:1)                                                         27    AlCl.sub.3 /High MW                                                                           15       2.8      1.66                                          DMDAAC (10:1)                                                            28    AlCl.sub.3 /Medium MW                                                                         15       3.0      --                                            DMDAAC (10:1)                                                            29    AlCl.sub.3 /Low MW                                                                            15       2.8      --                                            DMDAAC (10:1)                                                            ______________________________________                                          *Comparison Example                                                            .sup.+ AlCl.sub.3 is Hardwicke AlCl.sub.3 throughout Table I                   **Composition ratios in this table are on a product:product (As Product)       basis.                                                                   

EXAMPLES 30-84

In Examples 30-84, jar tests were run on feed water having a turbidity of approximately 12 NTU's. Total alkalinity was approximately 150 ppm.

The jar tests were run under the following conditions:

1 min @ 100 rpm

3 min @ 50 rpm

6 min @ 20 rpm

5 min @ 0 rpm

After a 5 minute settling period, 10 ml samples of supernatant were drawn, and turbidity was measured using a Bausch & Lom Mini-20 Spectrophotometer/Nephelometer.

Results are shown in Table II.

                                      TABLE II                                     __________________________________________________________________________                                    Active Dosage                                                                            Supernatant                           Example                        (As product dosage)                                                                      Clarity (NTU's)                       Number                                                                              Flocculant                (ppm)     (5 min.)                              __________________________________________________________________________     .sup. 30.sup.+                                                                      High MW Polyamine         0.5       8.6                                   31   High MW Polyamine         2.5       8.8                                   32   High MW Polyamine         10.0      8.8                                   33   High MW Polyamine         25.0      9.6                                   34   Low MW Polyamine          0.5       8.8                                   35   Low MW Polyamine          2.5       8.6                                   36   Low MW Polyamine          10.0      8.8                                   37   Low MW Polyamine          25.0      8.9                                   38   High MW PolyDMDAAC        0.4       9.4                                   39   High MW PolyDMDAAC        4.0       8.9                                   40   High MW PolyDMDAAC        8.0       9.0                                   41   High MW PolyDMDAAC        20.0      9.8                                   42   Medium MW PolyDMDAAC      0.4       9.2                                   43   Medium MW PolyDMDAAC      4.0       9.2                                   44   Medium MW PolyDMDAAC      8.0       9.0                                   45   Medium MW PolyDMDAAC      20.0      9.6                                   46   Low MW PolyDMDAAC         0.4       9.1                                   47   Low MW PolyDMDAAC         4.0       9.5                                   48   Low MW PolyDMDAAC         8.0       9.2                                   49   Low MW PolyDMDAAC         20.0      9.8                                   50   Dry PolyDMDAAC            1.0       9.6                                   51   Dry PolyDMDAAC            5.0       9.4                                   52   Dry PolyDMDAAC            10.0      9.4                                   53   Dry PolyDMDAAC            25.0      10.1                                  54   Hardwicke AlCl.sub.3      2.2       6.7                                   55   Hardwicke AlCl.sub.3      3.8       4.2                                   56   Hardwicke AlCl.sub.3      5.4       2.4                                   57   Hardwicke AlCl.sub.3      8.1       1.1                                   58   Reheis AlCl.sub.3         2.8       6.7                                   59   Reheis AlCl.sub.3         4.5       3.9                                   60   Reheis AlCl.sub.3         6.7       1.8                                   61   Reheis AlCl.sub.3         10.1      0.9                                   62   Courtney AlCl.sub.3       2.8       7.1                                   63   Courtney AlCl.sub.3       4.5       4.6                                   64   Courtney AlCl.sub.3       6.7       1.7                                   65   Courtney AlCl.sub.3       10.1      1.0                                   66   Vista AlCl.sub.3          2.7       7.4                                   67   Vista AlCl.sub.3          4.3       5.9                                   68   Vista AlCl.sub.3          6.5       2.7                                   69   Vista AlCl.sub.3          9.7       1.1                                   70   Hardwicke AlCl.sub.3                2.3                                   71   Hardwicke AlCl.sub.3 /High MW Polyamine (5:1)*                                                           (20)      4.9                                   72   Hardwicke AlCl.sub.3 /High MW Polyamine (10:1)                                                           (20)      2.8                                   73   Hardwicke AlCl.sub.3 /High MW Polyamine (20:1)                                                           (20)      1.4                                   74   Hardwicke AlCl.sub.3 /Low MW Polyamine (5:1)                                                             (20)      4.7                                   75   Hardwicke AlCl.sub.3 /Low MW Polyamine (10:1)                                                            (20)      2.8                                   76   Hardwicke AlCl.sub.3 /Low MW Polyamine (20:1)                                                            (20)      1.5                                   77   Hardwicke AlCl.sub.3 /High MW PolyDMDAAC (5:1)                                                           (20)      4.8                                   78   Hardwicke AlCl.sub.3 /High MW PolyDMDAAC (10:1)                                                          (20)      2.9                                   79   Hardwicke AlCl.sub.3 /High MW PolyDMDAAC (20:1)                                                          (20)      1.8                                   80   Hardwicke AlCl.sub.3 /High MW PolyDMDAAC (50:1)                                                          (20)      1.9                                   81   Hardwicke AlCl.sub.3 /Medium MW PolyDMDAAC (5:1)                                                         (20)      4.9                                   82   Hardwicke AlCl.sub.3 /Medium MW PolyDMDAAC (20:1)                                                        (20)      1.9                                   83   Hardwicke AlCl.sub.3 /Low MW PolyDMDAAC (5:1)                                                            (20)      5.0                                   84   Hardwicke AlCl.sub.3 /Low MW PolyDMDAAC (20:1)                                                           (20)      1.8                                   __________________________________________________________________________      .sup.+ Examples 30-70 are comparison examples.                                 *Composition ratios in this table are on a product:product (As Product)        basis.                                                                    

What is claimed is:
 1. A composition for reducing turbidity in aqueous systems comprising:(a) aluminum chloride; and (b) at least one water-soluble polymer selected from the group consisting of:(i) water-soluble polyamines represented by structure (I) ##STR2## wherein R₁ and R₂, which may be the same or different, are selected from the group consisting of straight or branched C₁ -C₈ alkyl, substituted straight or branched C₁ -C₈ alkyl and hydrogen; wherein R is selected from the group consisting of straight or branched C₁ -C₈ alkyl and substituted straight or branched C₁ -C₈ alkyl; and wherein n ranges from 2-50,000; and (ii) water-soluble C₁ -C₈ dialkyl diallyl ammonium polymers; wherein the weight ratio of (a):(b) is at least 20:1, on an active basis.
 2. The composition of claim 1, wherein (b) is an epichlorohydrin dimethylamine polymer.
 3. The composition of claim 1, wherein (b) is selected from the group consisting of polydimethyl diallyl ammonium chloride, polydiethyl diallyl ammonium chloride, polydimethyl diallyl ammonium bromide and polydiethyl diallyl ammonium bromide.
 4. The composition of claim 1, wherein (b) is polydimethyl diallyl ammonium chloride.
 5. A method for reducing the turbidity of an aqueous system comprising adding to said system an effective amount of a composition comprising:(a) aluminum chloride; and (b) at least one water-soluble polymer selected from the group consisting of:(i) water-soluble polyamines represented by structure I ##STR3## wherein R₁ and R₂, which may be the same or different, are selected from the group consisting of straight or branched C₁ -C₈ alkyl, substituted straight or branched C₁ -C₈ alkyl and hydrogen; wherein R is selected from the group consisting of straight or branched C₁ -C₈ alkyl and substituted straight or branched C₁ -C₈ alkyl; and wherein n ranges from 2-50,000; and (ii) water-soluble C₁ -C₈ dialkyl diallyl ammonium polymers; wherein the weight ratio of (a):(b) is at least 20:1.
 6. The method of claim 5, wherein (b) is an epichlorohydrin dimethylamine polymer.
 7. The method of claim 5, wherein (b) is selected from the group consisting of polydimethyl diallyl ammonium chloride, polydiethyl ammonium chloride, polydiethyl diallyl ammonium chloride, polydimethyl diallyl ammonium bromide and polydiethyl diallyl ammonium bromide.
 8. The method of claim 5, wherein (b) is polydimethyl diallyl ammonium chloride.
 9. The method of claim 5, wherein said aqueous system contains 0.1 weight percent, or less, suspended solids.
 10. The method of claim 5, wherein said effective amount is from about 0.1 to about 100 ppm of said composition. 